special sense Flashcards
receptor cells make up…
- Neuroepithelium: retina and olfactory Epithelium, sensory Neurons from neuroectoderm
- Sensoepithelium: taste buds and Epithelium in internal ear, Special epithelial cells from Surface ectoderm
- Sensory nerve ending (pacinian and Meisners corpuscle)
Ocular refractive media consists of
lens, chamber, vitreous humor
Accessory structures
eyelids, lacrimal Glands, extraocular muscles, conjunctiva
Developmental Sources of the eye
- Neural tube: retina, muscle of Iris
- Surface ectoderm: lens, anterior Epithelium of Cornea
- Head Mesenchyme: all others
Development of eye
3rd week:
- outpockenings –> vesicles attached by optic stalk –> optic Cup –> inner layer (muscle of Iris, neural of retina) and outer layer (Pigment of retina)
- lense Surface ectoderm –> lens placode –> lens vesicle –>lens
- optic stalk –> otpic nerve
6th week:
- hyaloid artery into optic Cup –> choroid fissue that Closes befire birth
Wall of the eyeball
FIBROUS LAYER
- Cornea
- sclera
VASCULAR LAYER
- Iris
- ciliary Body
- choroid
RETIANL LAYER
Cornea
avascular!!
- Stratified squamous non-keratinized Epithelium
- Anterior b.m. (bowman’s membrane)
- Stroma of dense collagenous tissue in lamellae
- Posterior b.m. (descemet’s membrane)
- Pre-Descemet’s membrane (Dua’s layer)
6- Endothelium
Sclera
- irregular dense collagenous tissue
- Collagen fibers and elastic fibers
- blood vessels and nerves
Cornoscleral Limbus: Junction of Cornea and sclera, canal of Schlemm
iris
- highly vascularized
- non-photosensitive retina on posterior Surface
sphincter pupillae muscle: smooth muscle cells near margin of Iris
dilator pupillae muscle: extends radially, composed of the processes of myoepithelial cells
Ciliary body
- smooth muscles
- inner Surface covered by non-photosensitive retina
Choroid
- pigmented loose CT
- absorbs light
- provides support and nutrients for retina
Parts of the retina
Photosensitive
Non-photosensitive
- iridial part (behind Iris)
- ciliary part (behind ciliary Body)
ora serrata: line between photosensitive and non-photosensitive retina
Microscopic structure of the retina
two layers:
- outer layer
- inner layer
Iridial part of the non-photosensitive retina
outer layer:
- 1 layer of pigmented myoepithelial cells (dilator pupillae muscle)
inner layer:
1 layer of pigmented cells
- -> Formation of dilator pupillae
- -> absorption of light
Ciliary part of non-photosensitive retina
outer layer:
1 layer of pigentocyti
inner layer:
1 layer of non-pigmented cuboidal cells
- ->Secretion of aqueous Humor
- ->Production of zonular fibers –> suspensory ligament of lens
Photosensitive retina is divided in:
outer layer
inner layer
Pigmented (outer) layer of photosensitive retina
- retinal pigement Epithelium (single layer of Pigemtocyti)
- Basement membrane
pigentocyti have microvilli on inner sruface that go between photoreceptors
Functions of retinal pigemtn epithelium
- absorbs light
- structural support
- metabolic support
- blood- retinal-barrier
- phagocytoses membranous Disc
- (re) Synthesis of rhodopsin
(Re) Synthesis of rhodopsin
Vitamin A –> Retinol –> retinal
retinal + opsin –> rhodopsin
Neural (inner) layer of photosensitive retina (Groups of Neurons)
Photoreceptor cells
Conducting cells
Ganglion cells
Photoreceptor cells are divided in:
rod cells
Cone cells
Structure of photoreceptor cells
bipolar Neurons
dendrite Body axon that Ends in: - sferule (rod) - pedicle (cone)
Dendrite of photoreceptor cell
- outer Segment
- Connecting cilium
- inner Segment
>outer part (mitochondria)
>inner part (Rhodopsin is synthesized)
Outer Segment of rod
- stack of flattened membranous Discs
- Discs are shed and phagocytosed by RPE
- light: retinal –> Retinol , release of opsin and changes in permeability of Plasma membranes
Functions of rods
- more sensitive to light
- during period of low light intensity –> Image of gray tones
Outer Segment of cone
- memranous Disc are continuous with Plasma membrane
three classe sof cones
L (Long) M (middle) S (short-wavelength)
Function of cones
- sensitive to red, green and blue regions of visual spectrum
Conducting cells of the retina
- bipolar cells
- horizontal cells
- Amacrine cells
Bipolar cells
Connections:
- photoreceptors and Ganglion cells
- photoreceptors and horizontal cells
- photoreceptors and amacrine cells
Horizontal cells
- connect rods and cones
- Synapse with bipolar cells
Amacrine cells
- no not have an axon!!!
- connect bipolar and Ganglion cells
Ganglion cells
- large, mulitpolar Neurons
- with bipolar cells
- with few amacrine cells
- axons pass into optic nerve Fiber layer and then to optic nerve
Supporting cells of the retina
Müller cells: type of astrocytes
- apical Ends form outer limiting membrane
- Basic parts together with b.m. form inner limiting membrane
functions: support, Transfer of metabolites, Regulation of electrolytes
10 histological layers of retina (PPOOOIIGLI)
1: Pigmented layer: RPE
2. Photoreceptor layer: outer and inner Segments
3. Outer limiting layer: apical Ends of Mülller cells
4 . Outer nuclear layer: cell bodies of photorecept,
5. Outer plexiform layer: processes of photo, horizontal and bipolar
6. Inner nuclear layer: cell bodies of conducting and Müller
7. Inner plexiform layer: processes of bipolar, amacrine and ganglion
8. Ganglion cell layer: cell bodies of ganglion
9. Layer of optic nerve fibers: axons of glangion cells
10. Inner limiting membrane: Basic Ends of Müller cells